A novel method to detect cathodic second-phase particles in Mg alloys

In this work, a new method for detecting cathodic second-phase particles on the Mg alloy surface has been developed based on in situ observation of the blade-abraded surfaces of AZ31, AZ61, and 99.9 % pure Mg during the immersion in concentrated alkaline solutions. Continuous local gas evolutions were observed at certain points on the blade-abraded surface, and second-phase particles were found at the same positions, revealing the presence of cathodic particles at the gas evolution sites. The continuous local gas evolution reaction was found to be coupled with not only oxide formation reaction on the Mg matrix around the cathodic particles but also dissolution of Mg at the area within 2–3 μm distance from the cathodic particle. The gas evolution rate appeared to be proportional to the size of cathodic particles, and various cathodic particles containing Fe, Mn, Al, and/or Si were found to be present in the Mg alloys. Based upon the experimental results, it is concluded that the new method is simple, fast, and non-destructive, and it can be used to detect all the cathodic second-phase particles present on the entire surface of Mg alloys, irrespective of the sample shape and size.